Generally, a tubular heat exchanger consists of a shell or large vessel with a bundle of tubes inside of the shell. Two fluids of different starting temperatures flow through the heat exchanger. The fluid with the higher starting temperature is known as the primary fluid and the fluid with the lower starting temperature is known as the secondary fluid. One primary fluid, known as the tube-side fluid, flows inside of the tubes while a second fluid, known as the shell-side fluid, flows outside of the tubes through the shell. The fluids may both be liquids, or they may both be gases, or one may be a gas while the other is a liquid. Furthermore, either of the primary fluid or the secondary fluid may be the tube-side fluid or the shell-side fluid. During operation of the heat exchanger, heat is transferred between the two fluids without direct contact between the two fluids. Specifically, heat is transferred from the primary fluid, through the walls of the tubes, and into the secondary fluid. The transfer of heat without contact between the shell-side fluid and the tube-side fluid is particularly desirable in the nuclear power plant industry because the primary or secondary fluids may become radioactive. Depending upon the fluids used and the desired results, heat is transferred either from the tube-side fluid to the shell-side fluid or vice versa.
The state-of-the art in flow arrangements for tubular heat exchangers generally indicates that the number of shell passes in industrial practice is restricted to two. A shell-side or tube-side pass in the art is considered to be the number of times that the fluid traverses the effective working length of the heat exchanger. If the demands of fluid flow rates and their terminal temperatures of the two heat exchanging streams cannot be satisfied in a single or two shell pass unit (or its close adaptations known as “spilt flow” and “divided flow” shown in the Tubular Exchanger Manufacturers Association or TEMA standards tables), then the designer is forced to utilize multiple heat exchanger shells each with internal tube bundles and use interconnecting pipes to fluidly coupled the shells together (see, e.g. FIG. 6). The multi-shell arrangement is poor design palliative, not in the least because it creates several external flanged joint connections that may leak during service. Multiplicity of shells also increases the plant's capital cost.
An improved heat exchanger is desired.